How jet engines are built to survive bird strikes

HostThere's a specialized tool engineers use that sounds like a total joke, but it's actually very real. It's called a chicken cannon. They use a large gas-powered gun to fire bird bodies at a spinning jet engine at hundreds of miles an hour. Why do we have to go to such lengths just to test for birds?

GuestWell, it's because of the sheer amount of air these engines need to work. Think about a massive engine on a big plane. When it's taking off, it pulls in about four thousand five hundred pounds of air every single second. That's a huge amount of weight moving very fast. All that suction creates an invisible column of air right in front of the engine. If anything enters that column, it's basically locked onto a path straight into the fan. Because planes move at hundreds of miles an hour during takeoff, a bird simply has no way to move out of the way once it's caught in that air. It's getting pulled in too fast to escape, so the engine has to be ready to deal with the hit.

HostSo the engine is basically a giant vacuum in the sky. But I always thought if a bird goes in, the whole thing would just stop working.

GuestIt's actually much harder to kill an engine than most people think. We usually assume a bird goes into the very heart of the engine where the fire and the gears are. But the big fan blades you see at the front act as a centrifuge. Since birds are much heavier than the air around them, the spinning motion of those blades flings them outward, away from the center. Most of the bird remains end up in the bypass duct, which is a big outer ring that wraps around the core of the engine. The bits just get spat out the back through that ring without ever touching the sensitive parts that actually make the power. This lets the engine keep burning fuel and pushing the plane forward like nothing happened.

HostWhat if it's a really big bird? A heavy bird hitting a blade that fast has to do some real damage.

GuestThat's exactly why the chicken cannon is so important. To be allowed to fly, an engine has to pass a test where they fire bird bodies or even blocks of jelly into it while it's running at over three hundred miles an hour. The rules are very strict. The engine has to be able to swallow that bird and still provide at least seventy-five percent of its full power for several minutes afterward. The goal is to give the pilot enough time and push to circle back and land the plane safely. It doesn't have to stay perfect forever, but it has to stay alive long enough to get everyone back on the ground.

HostBut if the hit is hard enough to actually snap one of those metal blades, doesn't that just destroy everything else?

GuestThat's the ultimate fear, and engineers have a plan for it called containment. The outer shell of the engine is wrapped in heavy-duty armor made of titanium or layers of Kevlar, which is the same stuff used in bulletproof vests. The engine is designed so that if a blade snaps off, the outer casing catches the metal pieces like a shield. This stops those pieces from flying out and hitting the wing or the main body of the plane where the passengers are. It keeps the failure inside the box so the rest of the aircraft stays whole and keeps flying.

HostSo the engine is basically wearing its own armor just in case a bird gets in the way.

GuestThe engines are built to take the hit, and those tests prove that even if everything inside breaks, that armored case keeps the whole plane safe.

HostThose big engines on the wing will look a bit different to me now that I know they're wearing a bulletproof vest.